Film image reading system and image processing method dot sequentially adjusting image parameters

ABSTRACT

The present invention achieves an exposure control for getting an image with the best SN without a mechanical iris and an image processing which is good at the color-reappearance and the gradation property with a simple digital processing circuit. When the film image is read by the line sensor 14 which has an electric shutter function, the electric shutter, the film feeding speed and the analog amplifier 16 are controlled totally so as to obtain images with the best SN from high to low transmittance negatives. And, when the dot sequential R, G, B digital signals are processed digitally, the offset values and the gain volumes of the respective R, G, B are calculated based on the maximum value and the minimum value which are detected by the respective R, G, B digital signals, the calculated offset values of the respective R, G, B are added to the dot sequential R, G, B digital signals which are obtained during the re-scanning, and the calculated gain volumes of the respective R, G, B are multiplied by the offset dot-sequential R, G, B digital signals so as to adjust the white balance and the black balance.

This application is a divisional of copending application Ser. No.08/416,315, filed on Apr. 4, 1995, the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film image reading system and animage processing method.

2. Description of the Related Art

Conventionally, a film scanner is proposed wherein an image of a film istaken in with a CCD line sensor (Japan Patent Application Laid-Open No.63-39267).

Usually, the exposure of the film scanner of this kind is controlled bya mechanical iris. And, there is no film scanner wherein the exposure iscontrolled by a electronic shutter of the CCD line sensor.

Further, when a negative image is converted into a positive image, thedispersion of the negative image becomes a problem, therefore, thesignal processing circuit in Japan Patent Application Laid-Open No.4-107082 copes with the problem by the analog processing. That is, therespective maximum and minimum levels of three color signals aredetected, and the variable gain amplification circuit and the leveladjustment circuit (clamper circuit), which are provided for two signalsrespectively, are adjusted so as to make the maximum and minimum levelsof three color signals equal to each other, whereby the white balanceand the black balance are adjusted.

And, in the signal processing circuit of Japan Patent ApplicationLaid-Open No. 4-107082, a gamma correction circuit for making thegradation property of three color signals is provided for every colorsignal. However, as to the negative image of which the exposure inphotographing is under or over, the gradation property differs and thegamma property differs also. Therefore, in the signal processing circuitof Japan Patent Application Laid-Open No. 4-107083, the image signalsare processed with the variable gamma so as to compensate the differenceof the gamma property by the scene. This signal processing is an analogprocessing, wherein variable gain amplification circuits arerespectively provided in the front and at the back of the gammacorrection circuit which has a knee property, and the gains of thesevariable gain amplification circuits are adjusted so as to change thegamma.

Now, when the exposure of the film scanner is controlled by a mechanicaliris, the structure of the iris becomes complex so that it is expensive.Moreover, the exposure control means is independent, so that there is aproblem in that it can not cope with the negative between the high andlow transmittance rate (that is, the negative from the over exposure tothe under exposure).

And, the conventional circuit for adjusting the white balance and theblack balance of the R, G, B signals is provided in the R, B signalprocessing system, and the negative-positive reversal circuit and thegamma correction circuit are provided in the respective R, G, B signalprocessing systems, therefore, there is a problem in that the processingcircuits are large and complex.

Further, the negative of the over exposure is different from thenegative of the under exposure in the gradation property to the subjectluminance, however, in the gamma correction of Japan Patent ApplicationLaid-Open No. 4-107083, the gamma is not changed in accordance with thesubject luminance, so that the coloring of the medium contract becomes aproblem.

SUMMARY OF THE INVENTION

The present invention has been developed to eliminate theabove-described disadvantages and has as its aim the provision of a filmimage reading system wherein the exposure can be controlled without amechanical iris from the high permeation rate negative to the lownegative so as to get the image of the best SN ratio.

And, the present invention has been developed to provide an imageprocessing method wherein the image which is excellent in the colorreproduction and in the gradation property by the simple digitalprocessing circuit.

To achieve the above-described object, a film image reading system inwhich a film, which is developed, for still photography is fed at aconstant speed, and an image of said film is read by a line sensor, andan output voltage of said line sensor is amplified by an analogamplifier so as to be outputted to an A/D convertor, said film imagereading system comprising: said line sensor for discharging anunnecessary electric charge stored in each receiving part when a shuttergate pulse is inputted, and for transferring an electric charge storedin said each receiving part to a shift resistor to be outputted as asequential voltage signal when a read gate pulse of one line cycle isinputted; first exposure control means for controlling an exposure timeby controlling a generating timing of said shutter gate pulse to saidread gate pulse; second exposure control means for controlling anexposure time by controlling a feeding speed of said film and changingcycles of said shutter gate pulse and said read gate pulse in proportionto said feeding speed; gain control means for controlling a gain of saidanalog amplifier; and, control means for controlling said first exposurecontrol means, a second exposure control means and said gain controlmeans based on an information showing a brightness of a film image to bescanned in a manner that an input voltage of said A/D convertor during ascanning of said film image becomes an optimal condition.

And, an image processing method in which a film, which is developed, forstill photography is fed at a constant speed, and an image of said filmis read by a line sensor, an output voltage of said line sensor isconverted into dot-sequential R, G, B digital signals by a A/Dconvertor, and then the R, G, B digital signals are digital-processed,said image processing method comprising; (a) step of detecting referencemaximum values and reference minimum values of said R, G, B digitalsignals, respectively, while scanning one film image of the film and ofcalculating offset values and gain volumes of R, G, B respectively baseon the reference maximum values and the reference minimum values; (b)step of adding dot-sequential R, G, B digital signals outputted fromsaid A/D convertor during re-scanning of said one film image to saidoffset values, which are calculated, of R, G, B; and,(c) step ofmultiplying the dot-sequential R, G, B digital signals which are offsetby the gain volumes of R, G, B, respectively; wherein these steps areperformed so as to adjust a white balance and a black balance. And, animage processing method further comprises a step of negative-positivereversal by subtracting said dot-sequential R, G, B digital signals,which are offset, from a determined value showing a white peak levelbetween the (a) step and the (b) step. Further, a look-up table whichstores previous gamma correction values according to a signal level isarranged and gamma gains for extending or compressing said gammacorrection value by multiplying said gamma correction value are set forrespective colors, and after said (c) step, (d) step of readingsequentially a gamma correction value from said look-up table based onR, G, B digital signals which are input sequentially and of selecting agamma gain among gamma gains of said respective colors in accordancewith that said gamma correction value which is read corresponds to whatcolor digital signal; and, (e) step of applying a multiplication of saidgamma correction value which is read and said gamma gain which isselected and of subtracting a gamma correction value which is extendedor compressed by said multiplication from the R, G, B digital signalswhich are inputted sequentially; are performed so that a gammacorrection is achieved dot-sequentially by each color. Moreover, thegamma gain of each color is determined based on a brightness of saidfilm image.

According to this invention, a developed film for a still camera is fedat a constant speed and the image of the film is read by a line sensor,and then, when the output voltage of the line sensor is amplified by ananalog amplifier so as to be outputted to an A/D convertor, thefollowing three control means are controlled in a manner that the inputvoltage of the A/D convertor becomes optimal in its condition. That is,there is a first exposure control means for controlling an exposure timeby controlling the generating timing of the shutter gate pulse for theread gate pulse in a line sensor which has an electric shutter function,a second exposure control means for controlling an exposure time bycontrolling the film feeding speed and changing the cycles of theshutter gate pulse and the like so as to control the electric shutter inaccordance with the feeding speed and a gain control means forcontrolling the gain of the analog amplifier, and the three controlmeans are controlled totally based on the information showing thebrightness of the film image to be scanned, whereby the image with thebest SN can be obtained from a high transmittance negative to a lowtransmittance negative.

And, in an image processing method wherein a developed film for a stillcamera is fed at a constant speed and the image of the film is read by aline sensor, and the output voltage of the line sensor is converted tothe dot-sequential R, G, B digital signals by the A/D convertor so as todigital-process the R, G, B digital signals; the reference maximumvalues and the reference minimum values are detected respectively forthe R, G, B digital signals while scanning one film image and the offsetvalues and the gain volumes for R. G, B are calculated previously basedon the reference maximum values and the reference minimum values, andthen the calculated offset values for R, G, B are added to thedot-sequential R, G, B digital signals which are outputted from the A/Dconverter during the re-scanning of the one film image. Thereafter, theoffset dot-sequential R, G, B digital signals are multiplied by the gainvolumes for R, G, B so as to adjust the white balance and the blackbalance. And, the offset dot-sequential R, G, B digital signals aresubtracted from the determined values showing the white peak level so asto achieve the positive-negative reversal. Further, a look-up table, inwhich the gamma correction values corresponding to the signal levels arestored previously, is provided, and the gamma gain of each color forextending or compressing the gamma correction value is set bymultiplying the gamma correction value. And, the gamma correction valuesare sequentially read from the look-up table based on the R, G, Bdigital signals which are inputted sequentially and a gamma gain isselected among the gamma gains for the respective colors in accordancewith that the read gamma correction value which corresponds to whichcolor digital signal, the read gamma correction value and the selectedgamma gain are multiplied and the gamma correction values which areextended or compressed by the multiplication are subtracted from the R,G, B digital signals which are inputted dot-sequentially, whereby thegamma correction is achieved for each color dot-sequentially. And, thegamma gain of each color is determined based on the brightness of thefilm image, therefore, a good gray balance can be achieved in mediumcontrast whether it is an under negative or an over negative.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of this invention, as well as other aims and advantagesthereof, will be readily apparent from consideration of the followingspecification relating to the accompanied drawings, in which likereference characters designate the same or similar parts throughout thefigures thereof and wherein:

FIG. 1 is an essential block diagram showing one embodiment of the filmscanner according to the present invention;

FIG. 2(A) is a view showing each integrating area integrated in theintegrating block shown in FIG. 1 and FIG. 2(B) is a view showing eacharea for calculating a photometric value;

FIG. 3 is a graph showing one embodiment in a case that an electronicshutter, a film feeding speed and an amplifier gain are controlledtotally;

FIG. 4 is a graph showing another embodiment in a case that anelectronic shutter, a film feeding speed and an amplifier gain arecontrolled totally;

FIG. 5 is an essential block diagram showing another control method ofthe timing generator shown in FIG. 1;

FIGS. 6(A)-B(D) are graphs showing the processing contents at each partof the digital signal processing circuit in FIG. 1;

FIGS. 7(A)-7(C) are graphs for explaining the gamma correction methodaccording to the present invention;

FIG. 8 is a block diagram showing the detailed structure of the digitalsignal processing circuit in FIG. 1; FIG. 9(A)-9(H) are timing charts ofsignals at each part in FIG. 1;

FIGS. 10(A) and 10(B) are graphs showing the relation between thesubject brightness and the CCD output; and,

FIGS. 11(A)-11(C) are graphs showing the gradation property, the gammaproperty and the base LUT to the subject brightness of the differentexposure negatives.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A detailed description will hereafter be given of the preferredembodiment of a film image reading system and an image processing methodaccording to the present invention with reference to the accompanyingdrawings.

FIG. 1 is an essential block diagram showing one embodiment of the filmscanner according to the present invention. This film scanner includes alight source 10 for illuminating, a taking lens 12, a CCD line sensor14, an analog amplifier 16, an A/D converter 18, a digital signalprocessing circuit 20, a motor 31, a film driving system including acapstan 32 and a pinch roller 33, a central processing unit (CPU) 40 andthe like.

The light source 10 illuminates a developed negative film 52 pulled outfrom a film cartridge 50 through an infrared cutting filter not shown,and the transmitted light through the film 52 is focused on thereceiving surface.

In the CCD line sensor 14, receiving parts for 1024 picture elements arearranged in the direction perpendicular to the film feeding direction,and the image light focused on the receiving surface of the CCD linesensor 14 is stored by charge in each receiving part by providing R, G,B filters so as to be converted to the R, G, B signal charges inaccordance with the brightness. When a read gate pulse with one linecycle, which is sent from the CCD driving circuit 15, is added, thestored R, G, B charges are transferred to the shift resistor andoutputted as a sequential voltage signal by the resistor transmissionpulse. And, in the CCD line sensor 14, a shutter gate and a shutterdrain are arranged adjacent to each receiving part, and the shutter gateis driven by the shutter gate pulse whereby the charges stored in thereceiving part can be sent out to the shutter drain. That is, the CCDline sensor 14 can control the charges to be stored in the receivingpart in accordance with the shutter gate pulse from the CCD drivingcircuit 15, what is called an electronic shutter function.

The R, G, B voltage signals which reads out from the CCD line sensor 14are clamped by a CDS clamp, not shown, and sent to the analog amplifier16 to control the gain which will be described later. The R,.G, Bvoltage signals for one frame, which are output from the analogamplifier 16, are converted to the dot sequential R, G, B digitalsignals and are applied with the white balance, the black balance, thenegative-positive reversal, the gamma correction and the like,thereafter, are stored in an image memory, not shown.

And, the R, G, B digital signals for one frame stored in the imagememory are read out repeatedly and are converted to the analog signalsby the D/A converter, and then are converted to the NTSC type compoundimage signals so as to output to the TV monitor. Therefore, the filmimage can be monitored on the TV monitor.

The film driving system is composed of a film supply part which isengaged with the spool 50A of the film cartridge 50 and drives the spool50A clockwise/counterclockwise, a film winding part for winding the film52 fed from the film feeding part, and means placed in the film feedingpath for conveying the film 52 by putting the film 52 between thecapstan 32 driven by the motor 31 and the pinch roller 33 at a desiredspeed. And, in the film supply part, the spool 50A of the film cartridge50 is driven clockwise in FIG. 1 so as to send the film 52 from the filmcartridge 50 until the film end is wound by the film winding part.

The CPU 40 controls the normal rotation/reversal rotation and thestart/stop of the motor 31 and the film feeding speed by the pulse widthmodulation via the motor rotation frequency/ direction control circuit34. For example, when the feeding speed is set at 9.25 mm/sec. whiletaking in a standard film image, the speed can be controlled from thelow speed of the half standard speed (4.625 mm/sec.) to the high speedof 16 times speed (148.0 mm/sec.). And, the number of the image elementsin the same direction as the film feeding direction for one framechanges in accordance with the film feeding speed when the cycle of theread gate pulse and the like in the CCD driving circuit 15 is notchanged, for example, the number of the image elements at the half, one,eight and 16 times speed are 1792, 896, 112 and 56 image elements,respectively.

Next, an explanation will be given of the exposure control method of thefilm scanner according to the present invention.

First, the film cartridge 50 is set in a cartridge storage part (notshown), and when the film 52 is sent out from the film cartridge 50 andthe film end is wound around the winding axis of the film winding part(the film loading is completed), the film 52 is pre-scanned. That is,the film 52 is fed at a high speed of 16 times in the sequentialdirection (in the right direction of FIG. 4), and rewound in thereversal direction at the high speed of 16 times. While pre-scanning,the dot-sequential R, G, B digital signals are taken in the integratingblock 41 through the CCD line sensor 14, the analog amplifier 16 and theA/D converter 18.

The film feeding speed is 16 times, so that the number of the imageelements in the film feeding direction for one frame is 56. The CCD linesensor 14 has receiving parts for 1024 image elements in the directionperpendicular to the film feeding direction, as described above, and thereceiving parts are thinned down one thirty-second whereby the number ofthe image elements in the direction perpendicular to the film feedingdirection for one frame is 32. FIG. 2(A) shows integrating areas in theintegrating block 41 of the film image for one frame. That is, one frame(56×32 image elements) is divided into 8×8 integrating areas, and theintegrating block 41 integrates the digital signal every integratingarea and outputs the integrated value to the CPU 40. And, oneintegrating area includes 7×4 image elements.

The CPU 40 calculates the six average luminance values for therespective areas in accordance with the integrated value from theintegrating block 41 as shown in FIG. 2(B). The average luminance valueof the central area 1 and the luminance value of the peripheral area,which is close to the average luminance area, are added and averaged,whereby the photometric value for the exposure control is calculated.The average luminance value of the central area 1 is weighted more thanthe luminance value of the peripheral areas.

The CPU 40 calculates the photometric values showing the brightness ofthe respective frames as described above, and these photometric valuesare stored in the random access memory (RAM) 40A built in the CPU. Thephotometric values for the respective frames are used for the exposurecontrol during the main-scanning of each frame.

Now, the exposure control according to the present invention is achievedin accordance with the following three means.

The CCD line sensor 14 has the electronic shutter function as describedabove, the shutter value is controlled through the CCD driving circuit15 from the CPU 40, so that the exposure time is controlled. And, inthis embodiment, the variable range of the shutter value of the electricshutter is 20%-100%.

Further, during the main-scanning, the CPU 40 can control so as to feedthe film 52 at a desired speed from one to half speed via the motorrotation frequency/direction control circuit 34 and the motor 31. A disc35 with slits is fitted to the axis of the motor 31, and a photodetector 36 for detecting the silts of the disc 35 outputs the pulsesignal showing the rotation speed of the motor to the timing generator37. During the main-scanning, the timing generator 37 generates a pulsesignal, which is synchronous with the rotation of the motor 31, by theinput pulse signal. The pulse signal which is generated from the timinggenerator 37 is added to the CCD driving circuit 15, the A/D converter18, a digital signal processing circuit 20 and the like, whereby therespective circuits are controlled as to the driving speed and aresynchronized.

That is, by changing the film feeding speed, the cycles of the read gatepulse, the shutter gate pulse and the resistor transmission pulse, whichare output from the CCD driving circuit 15 to the CCD line sensor 14,are changed automatically. Further, during the main-scanning at aregular speed, the number of the image elements in the same direction asthe film feeding direction of one frame becomes 896, and when the filmfeeding speed is changed, the cycles of the read gate pulse and the likeof the CCD driving circuit 15 are changed automatically, so that thenumber of the image elements does not change.

The film feeding speed is changed from regular to half, whereby theexposure time can be changed between 100% and 200%. Further, the controlmethod of the timing generator 34 is not limited to the aboveembodiment, as shown in FIG. 5, the reference clock frequency of thetiming generator 37 may be changed in accordance with the motor rotationspeed by the phase synchronous loop (PLL) 38.

Further, in the analog amplifier 16, which is arranged at the next partof the CCD line sensor 14, the gain is controlled by the gain controlsignal from the CPU 40, and in this embodiment, the amplifier gain canvary between 6 dB and 18 dB (2-8 times). The lowest gain of the analogamplifier 16 can be determined in accordance with the following formula;

    A/D converter rated input voltage lowest gain=min(CCD rated output voltage, analog amplifier rated input voltage).

Further, hereinunder, min(CCD rated output voltage, analog amplifierrated input voltage) is called a CCD proper output voltage. When the CCDoutput is equal to the CCD proper output voltage and the amplifier gainis set at the lowest gain, the input voltage to the A/D converter 18becomes proper (rated input voltage), so that the SN becomes best.

Next, an explanation will be given of a case that the electronicshutter, the film feeding speed and the amplifier gain of the CCD linesensor are controlled totally based on the photometric value of theframe will be main-scanned.

FIG. 3 is a graph showing one embodiment of the case in that theelectronic shutter, the film feeding speed and the amplifier gain arecontrolled totally and shows the change of the set value of eachparameter to the negative exposure value (photometric value) and therelation of the MAX output voltage of the CCD line sensor. As shown inFIG. 3, the under negative has a high transmittance, therefore, thenegative feeding speed is set at a regular speed and the gain of theanalog amplifier is set at the lowest gain (6 dB), whereby the CCDoutput voltage is adjusted to the CCD proper output voltage only by thecontrol with the electronic shutter. And, the open rate of the electricshutter is increased as the negative becomes over (the negativetransmittance lowers) so as to correspond to the lowering of thetransmittance.

When the open rate of the electronic shutter becomes 100%, thereafter,the receiving value (the exposure time) of the CCD line sensor 14 isadjusted by the negative feeding speed. That is, the open rate of theelectronic shutter is fixed at 100% to set the amplifier gain at thelowest gain and the feeding speed lowers as the negative becomes over.

When the adjustment range by the feeding speed gets to the limitation(half speed) and the negative becomes over, the open rate of theelectronic shutter is set at 100% and the feeding speed is fixed at thelowest speed (half speed), and only the analog gain is adjusted so thatthe input voltage of the A/D convertor 18 becomes proper (rated inputvoltage). And, in FIG. 3, the area is divided into 1,2,3, and the area 1shows the adjustment area only by the electronic shutter, the area 2shows the adjustment area only by the feeding speed and the area 3 showsthe adjustment area only by the analog amplifier gain. As shown in FIG.3, in the areas 1,2, the MAX output voltage of the CCD line sensor isthe CCD proper output voltage (constant), the best SN can be obtained.In the area 3, the amplifier gain of the analog amplifier is compensatedfor the MAX output voltage of the CCD line sensor which does not reachthe CCD proper output voltage, therefore, the SN lowers as the negativebecomes over. However, the maximum rated input range of the A/Dconverter is used, so that the resolution in the A/D conversion does notbecome lower.

FIG. 4 shows a graph of another embodiment of a case in that theelectronic shutter, the film feeding speed and the amplifier gain arecontrolled totally. In this embodiment, the negative feeding speed isvaried not continuously but in two steps including a regular speed and ahalf speed. Further, the adjustments in the areas 1,3 are the same asthat of the embodiment in FIG. 3, therefore, an explanation will begiven of the adjustment in the area 2.

When the open rate of the electronic shutter becomes 100% and thecontrol moves to that in the area 2, the negative feeding speed islowered to a half speed immediately and the open rate of the electricshutter, which has reached 100% once, is returned to 50%. And, in thestate that the negative feeding speed is fixed at a half speed, the CCDoutput voltage is adjusted so as to become the CCD proper output voltageby the control of the electronic shutter. And, when the negative becomesover and the open rate of the electronic shutter becomes 100% again,thereafter, the adjustment by the analog amplifier gain in the area 3 isperformed.

And, the negative feeding speed is switched in two steps, so that thetiming generator 37 can be simple. That is, the reference clockfrequency is used or divided into 1/2 without synchronizing with therotation of the motor 31 and/or using PLL, whereby the timing signal canbe generated in accordance with the switching of the negative feedingspeed. However, when the image is read in the area 2, there is a problemin that the scanning speed decreases compared with the case in FIG. 3.

Next, an explanation will be given of the digital signal processingcircuit 20 for the white balance, the black balance, thenegative-positive reversal, the gamma correction and the like.

First, the explanation will be given of the calculating method of theoffset value and the gain value for adjusting the white balance and theblack balance.

The CPU 40 inputs histogram values, which are obtained through theintegrating block 41 during the pre-scanning, and detects the respectivereference maximum values and the respective minimum values for R, G, Bamong these histogram values. And, an offset value and a gain volume canbe calculated based on the reference maximum value and the referenceminimum value in accordance with the following formulas;

    offset value=1023-R.sub.max                                (1)

    gain volume=1023 / (R.sub.max -R.sub.min)                  (2)

Further, the formulas (1) and (2) relate to R, however, another colorchannel is calculated similarly. Here, the R, G, B digital signals areshown with 10 bits, and 1023 is the maximum value thereof.

And, the original R_(org), which is outputted from the A/D convertor 18during the main-scanning, is added with the offset value of R as thefollowing formula;

    R1=R.sub.org +offset value                                 (3)

whereby a digital signal R1 which is black-point-offset is obtained. Theoriginals for G, B are treated similarly, whereby the peak values (blackof positive image) of the R, G, B digital signals are corresponded (seeFIG. 6(A)).

Then, the offset digital signal R1 is calculated as the followingformula;

    R2=1023-R1                                                 (4)

whereby the negative-positive reversal is performed (see FIG. 6(B)).

Next, the digital signal R2 which is applied with the negative-positivereversal is multiplied by the gain volume calculated with the formula(2) as the following formula;

    R3=R2×gain volume                                    (5)

whereby the other peak values (white of positive image) of the R, G, Bdigital signals are corresponded (see FIG. 6(C)).

Lastly, the R, G, B digital signals, which are multiplied by the gainvolumes, are applied with the respective gamma corrections, whereby thegray is adjusted (see FIG. 6(D)).

Next, a detailed explanation will be given of the gamma correction.

First, a look-up table (hereinunder, called a base LUT) is prepared forthe reference of the gamma correction.

The base LUT has a difference value (gamma correction value) which thereal look-up table (hereinunder, called a real LUT) showing a suitablegamma property is subtracted from the function y=x as shown in FIG.7(A). The base LUT is multiplied by the gamma gain, whereby the base LUTcan be changed (see FIG. 7(B)). A suitable gamma gain is multiplied fromone base LUT, whereby the LUT, of which the gamma correction values areextended or compressed by the respective R, G, B, can be obtained. And,the LUT, of which the gamma correction value is extended or compressedby the respective R, G, B, is subtracted from the function y=x, wherebythe real LUT for the respective R, G, B can be obtained (see FIG. 7(C)).

Therefore, the white balance and the black balance are adjusted inaccordance with the above formulas (3)-(5), and when the dot sequentialR, G. B digital signals, which are reversed positively-negatively, areapplied with the gamma correction, the sequential gamma correction valueis read from the base LUT based on the dot sequential R, G, B digitalsignals, the gamma correction value is multiplied by the gamma gain ofeach R, G, B so as to obtain the suitable extended or compressed gammacorrection value and the extended or compressed gamma correction valueof each color is subtracted from the dot sequential R, G, B digitalsignal, so that the gamma correction can be performed dot-sequentiallyby each color.

FIG. 8 is a block diagram including the internal structure of thedigital signal processing circuit 20 shown in FIG. 1. The digital signalprocessing circuit 20 processes digital signals as described above andincludes adders 21, 22, 24, multipliers 23, 26 and a base LUT 25. Thedot sequential R, G, B digital signal CMPAD is input to the adder 21from the A/D converter 18. And, as shown in FIG. 9(A) the digital signalCMPAD follows in time series R, G, B, G in accordance with the clockCHCLK (FIG. 9(B)).

On the other hand, the CPU 40 calculates the offset values (R_(offset),G_(offset), B_(offset)) and the gain volumes (R_(wbgain), G_(wbgain),B_(wbgain)) for each R, G, B so as to store them, and stores the gammagains (R_(gamgain), G_(gamgain), B_(gamgain)) for each R, G, B. And, theoffset value and the like are stored for every frame. And, the offsetvalue and the like corresponding to a frame to be main-scanned areselected by an address decoder 42, the R, G, B offset values are storedin resistors 43R, 43G, 43B by the INTDATA in FIG. 8, the R, G, B gainvolumes are stored in resistors 44R, 44G, 44B and the R, G, B gammagains are stored in resistors 45R, 45G, 45B. And, these are kept in theresistors until the R,G, B digital signals for one frame are processed.

The offset values (R_(offset), G_(offset), B_(offset)) stored in theresistor 43R, 43G, 43B are added to a multiplexer 46, and timing signalsINTCOLSL 0, 1 (FIGS. 9(C), 9(D)) which are made by dividing the clockCHCLK (FIG. 9(B)) are added to another input of the multipulexer 46. Themultiplexer 46 selects one offset value among three offset values by thetiming signal INTCOLSL 0, 1, and the selected offset value (FIG. 9(E))is outputted to another output of the adder 21 in the digital signalprocessing circuit 20.

Similarly, a multiplexer 47 selects one gain volume among three gainvolumes (R_(wbgain), G_(wbgain), B_(wbgain)) input from the resistors44R, 44G, 44B and outputs the selected gain volume (FIG. 9(F)) to themultiplier 23, and a multiplexer 48 selects one gamma gain among threegamma gains (R_(gamgain), G_(gamgain), B_(gamgain)) input from theresistors 45R, 45G, 45B and outputs the selected gamma gain (FIG. 9(G))to the multiplier 26.

On the other hand, the digital signal CMPAD (FIG. 9(A))is inputted tothe adder 21 as described above and the adder 21 adds the digital signalCMPAD with the offset value. With this arrangement, the digital signal,which is black point offset, can be obtained (see formula (4), FIG.6(A)).

The digital signal, which is output from the adder 21 and black pointoffset, is added to the negative input of the adder 22 the value (1023)showing a white peak level is added to the positive input of the adder22, and the adder 22 subtracts the black point offset digital signalfrom 1023. The negative-positive reversed digital signal can be obtained(see formula (5), FIG. 6(B)).

Then, the negative-positive reversed digital signal is provided to themultiplexer 23. The gain volume is provided to another input of themultiplier 23 from the multiplexer 47, and the multiplier 23 multipliestwo inputs so as to adjust the white of the positive image of the R, G,B digital signals (see formula (6), FIG. 6(C)).

Next, the digital signal, which is outputted from the multiplier 23, isprovided to the adder 24 and the base LUT 25. The base LUT 25 has thegamma correction value according to the input level as shown in FIG.7(A), reads out the gamma correction value in accordance with the inputdigital signal and outputs the gamma correction value to the multiplier26. The gamma gain is supplied to another input of the multiplier 26from the multiplexer 48, and the multiplier 23 multiplies two inputs,whereby the gamma correction values of the R, G, B digital signals forthe respective colors are generated and outputted to the negative inputof the adder 24. Further, the base LUT 25 has a compressed gammacorrection value and the gamma correction value is extended suitablywith the gamma gain of each color.

The adder 24 subtracts the gamma correction value which is extendedsuitably by each color from the R, G, B digital signal. In this way, theregular R, G, B digital signal RGBG_(gam) (FIG. 9(H)) can be obtained.

FIG. 10 is a graph showing the relation between the subject luminanceand the CCD output. In an usual screen, as shown in FIG. 10(A), there iscolorless gray, that is, white and black in the maximum area and theminimum area of the subject luminance. However, practically, all scenesdo not meet this, for example, there is no R component of the subject inthe maximum area of the subject luminance, so that there is a case inthat only the CCD output of R becomes larger than that of G, B.

In this embodiment, the CPU 40 detects the reference maximum values andthe reference minimum values of the respective R, G, B from the values,which are calculated from the histogram values, and calculates theoffset value and the gain volume with the detected values, however, thepresent invention should be not limited to this, the differences betweenthe reference maximum values and the reference minimum values, that is,R_(max) -R_(min), G_(max) -G_(min), G_(max) -G_(min) are calculated, andthe maximum values and the minimum values are reset in a manner thatthese values becomes close to each other and the offset values and thegain values may calculated in accordance with the formulas (1), (2).With this method, the screen shown in FIG. 10 (B) can becolor-reappeared well..

And, the different exposure negative differs in the gradation propertyto the subject luminance as shown in FIG. 11(A), and the gamma propertydiffers as shown in FIG. 11(B). Therefore, the base LUT must be changedin accordance with the exposure value of the negative as shown in FIG.11 (C).

Then, the the photometric value, which is detected for the exposurecontrol, is used so as to change the gamma gain (R_(gamgain),G_(gamgain), B_(gamgain)) of each color, whereby the gamma correctioncan be applied in accordance with the exposure value of the negative.

As described above, according to the film image reading system of thepresent invention , the electric shutter of the line sensor, the filmfeeding speed and the amplifier gain are controlled totally so as tocontrol the exposure, therefore, image signals with best SN can beobtained from a high transmittance negative to a low transmittancenegative without a mechanical iris. And, according to the imageprocessing method of the present invention, the digital processing isperformed in time series and dot sequentially, so that the structure ofthe digital signal processing circuit for a white balance, a blackbalance a negative-positive reversal, a gamma correction and the likecan be simple, therefore, the cost can be reduced, and the base LUT ismultiplied by the gamma gain so as to generate the various gammacorrection values, so that there are advantages in that only one baseLUT is needed and the memory volume can be reduced. Further, the gammacorrection is performed in accordance with the negative exposure volume,so that a good color-reappearance can be achieved without coloring ofmedium contrast.

It should be understood, however, that there is no intention to limitthe invention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

We claim:
 1. A gamma corrector for correcting R, G, B digital signals ofa film image which are input sequentially comprising:a reading systemreading the film image and outputting R, G, B, digital signals; alook-up table in which a base gamma correction value according to asignal level is stored previously; a gamma gain setter setting gammagain of each color for extending or compressing said base gammacorrection value; a reader reading said base gamma correction valuesequentially from said look-up table based on said R, G, B digitalsignals which are input sequentially; a selector selecting a gamma gainamong gamma gains of respective colors in accordance with a colordigital signal corresponding to said base gamma correction value outputby said reader; a multiplier multiplying said base gamma correctionvalue output from said reader and said gamma gain output by saidselector to output a real gamma correction value; and a subtractorsubtracting said real gamma correction value output by said multiplierfrom said R, G, B digital signals which are input sequentially, therebyproviding gamma correction dot-sequentially for each color.
 2. The gammacorrector according to claim 1, wherein said gamma gain setter includesmeans for varying the gamma gain of each color in accordance with abrightness of the film image.
 3. An image processing method in which afilm, which is developed, for still photography is fed at a constantspeed, an image of said film is read by a line sensor, an output voltageof said line sensor is converted into dot-sequential R, G, B digitalsignals by a A/D convertor, and then said R, G, B digital signals aredigital-processed, said image processing method comprising;(a) step ofdetecting reference maximum values and reference minimum values of saidR, G, B digital signals, respectively, while scanning one film image ofsaid film and of calculating offset values and gain volumes of R, G, Brespectively base on said reference maximum values and said referenceminimum values; (b) step of adding dot-sequential R, G, B digitalsignals outputted from said A/D convertor during re-scanning of said onefilm image to said offset values, which are calculated, of R, G, B; and,(c) step of multiplying said dot-sequential R, G, B digital signalswhich are offset by said gain volumes of R, G, B, respectively;whereinthese steps are performed so as to adjust a white balance and a blackbalance.
 4. An image processing method as set forth in claim 3, furthercomprising a step of negative-positive reversal by subtracting saiddot-sequential R, G. B digital signals, which are offset, from adetermined value showing a white peak level between said (a) step andsaid (b) step.
 5. An image processing method as set forth in claim 3,wherein said reference maximum values and said reference minimum valuesin said (a) step are calculated among m×n integrated values obtainedfrom a integrating block for integrating each picture element groupwhich one image plane is divided into m×n.
 6. An image processing methodas set forth in claim 3, wherein a look-up table which previously storesa gamma correction value according to a signal level is arranged andgamma gains for extending or compressing said gamma correction value bymultiplying said gamma correction value are set for respective colors,and after said (c) step,(d) step of reading sequentially a gammacorrection value from said look-up table based on R, G, B digitalsignals which are inputted sequentially and of selecting a gamma gainamong gamma gains of said respective colors in accordance with that saidgamma correction value which is read corresponds to what color digitalsignal; and, (e) step of applying a multiplication of said gammacorrection value which is read and said gamma gain which is selected andof subtracting a gamma correction value which is extended or compressedby said multiplication from said R, G, B digital signals which areinputted sequentially;are performed so that a gamma correction isachieved dot-sequentially by each color.
 7. An image processing methodas set forth in claim 6, wherein said gamma gain of each color isdetermined based on a brightness of said film image.
 8. A method forgamma correcting R, G, B digital signals of a film image which are inputsequentially comprising:reading the film image and outputting sequentialR, G, B, digital signals therefrom; providing a look-up table in which abase gamma correction value according to a signal level is storedpreviously; setting gamma gain of each color for extending orcompressing said base gamma correction value; reading said base gammacorrection value sequentially from said look-up table based on saidsequential R, G, B digital signals; selecting a gamma gain among gammagains of respective colors in accordance with a color digital signalcorresponding to said gamma correction value which is read; multiplyingsaid base gamma correction value which is read and said gamma gain whichis selected to form a real gamma correction value; and subtracting saidreal gamma correction value formed by said multiplying from saidsequential R, G, B digital signals so that a gamma correction isachieved dot-sequentially by each color.
 9. An image processing methodas set forth in claim 8, wherein said setting includes varying saidgamma gain of each color based on a brightness of said film image. 10.An image processor for developed film for still photographycomprising:means for feeding developed film; a line sensor reading animage of said film; an A/D convertor converting an output voltage fromsaid line sensor into dot-sequential R, G, B digital signals; a detectordetecting reference maximum values and reference minimum values of saidR, G, B digital signals, respectively, while scanning one film image ofsaid film; a calculator calculating offset values and gain volumes of R,G, B respectively based on said reference maximum values and saidreference minimum values; an adder adding dot-sequential R, G, B digitalsignals output from said A/D convertor during re-scanning of said onefilm image to said offset values, which are calculated, of R, B, G; anda multiplier multiplying said dot-sequential R, G, B digital signalsoutput from said adder by said gain volumes of R, G, B, respectively,wherein said detector, said calculator, said adder and said multiplieradjust a white balance and a black balance.
 11. The image processor asset forth in claim 10, wherein said adder further includes a subtractorsubtracting said dot-sequential R, G, B, digital signals which have beenadded to said offset values from a determined valued indicating a whitepeak level.
 12. The image processor as set forth in claim 10, furthercomprising:a look-up table in which a base gamma correction valueaccording to a signal level is stored previously; a gamma gain settersetting gamma gain of each color for extending or compressing said basegamma correction value; a reader reading said base gamma correctionvalue sequentially from said look-up table based on said R, G, B digitalsignals which are input sequentially; a selector selecting a gamma gainamong gamma gains of respective colors in accordance with a colordigital signal corresponding to said base gamma correction value outputby said reader; a multiplier multiplying said base gamma correctionvalue output from said reader and said gamma gain output by saidselector to output a real gamma correction value; and a subtractorsubtracting said real gamma correction value output by said multiplierfrom said R, G, B digital signals which are input sequentially, therebyproviding gamma correction dot-sequentially for each color.